Many biological polymers are electrically charged and will therefore migrate when placed in an electrical field. One very useful way to separate a mixture of different macromolecules as well as to characterize them is by their rate of movement in an electrical field. This property has been used to determine protein molecular weights; to distinguish among molecules by virtue of their individual net electrical charge; to detect amino acid changes from charged to uncharged residues or vice versa; and to separate different molecular weight species quantitatively as well as qualitatively. The overall technique, apparatus, and theory of such separations has become well established as electrophoresis.
A common used form of electrophoresis is zone electrophoresis, in which a sample is applied as a spot or band and the particles migrate through a solvent that is almost always supported by a homogeneous medium such as paper or a polymerized gel. This type of electrophoresis is used to analyze mixtures of molecules; to determine the purity of a single species of molecule; to assay for changes in mobility and/or confirmation; and for purification and separation of a mixture of different molecules into individual species. More complete and detailed information regarding the basic types of electrophoresis and the many applications for which each type of electrophoresis is utilized may be found in Freifelder, D., Physical Biochemistry, Applications to Biochemistry and Molecular Biology, 2nd edition, W. H. Freeman and Compnay, New York, 1982, pages 276-322.
Gel electrophoresis methods and electrophoretic apparatus which utilizes gels such as starch, polyacrylamide, agarose, and agarose-acrylamide as supporting media are well established and highly favored techniques used by investigators in research and industry. Gel electrophoresis provides the user with enhanced resolution and separation of mixtures of macromolecules, particularly proteins and nucleic acids such as deoxyribonucleic acid (hereinafter "DNA") and ribonucleic acid (hereinafter "RNA"). The variety of different applications and the value of gel electrophoresis as a superior analytical and/or preparative tool is demonstrated by the many innovations in apparatus for electrophoresis. These are exemplified by U.S. Pat. Nos. 3,047,489; 4,234,400; 4,151,065; 3,980,546; 3,980,540; 3,932,265; and 3,553,097.
The resolution of DNA and RNA molecules by molecular weight using gel electrophoresis apparatus prominently identifies one of the long standing, recurring problems of electrophoretic analyses. Typically, to obtain a good separation of DNA and other large molecular weight compositions (proteins and nucleic acids), electrophoresis must be performed on an extended time basis, typically 16-24 hours in duration. One of the constant problems of long term electrophoretic analysis is the breakdown of the buffer used to control the pH of the medium due to the formation of acid (H.sup.+) at the anode and the formation of base (OH.sup.-) at the cathode. This problem is usually resolved by circulating the buffer fluid between the anode containing buffer chamber and the cathode containing buffer chamber using a mechanical pump. While adequate to correct the problem, such external mechanical pumps are typically expensive, awkward to utilize within the limited confines of electrophoretic apparatus, and are subject to mechanical breakdown. For these reasons, it is generally accepted and recognized that any improvement in electrophoretic apparatus which would avoid using an external mechanical pump and yet provide for the circulation of buffer within the apparatus to eliminate pH differences between the anode and cathode chambers, would be regarded as a welcome and substantive advance.